Parkinson disease (PD) is a common disease of the elderly associated with substantial morbidity and early mortality. The causes of PD are largely unknown, but recent studies in small cohorts have implicated occupational exposure to neurotoxic solvents. Demonstrating a relation in a larger study would provide an opportunity to reduce exposures and hence disease risk. This is particularly important given the lack of any definitive pharmacotherapy to slow disease progression. Moreover, prevention would not be limited to workers with high exposures such as painters, mechanics, metal workers and plastic workers, since solvents are common environmental air and water pollutants in urban areas of the US. This proposal investigates the relation between occupational solvent exposure and incident PD in a large and efficiently-constructed, population-based study using existing data in Finland. Finland is an ideal country in which to conduct the studies described below due to low migration/immigration, universal health care, PD diagnoses made by neurologists, and high patient compliance with treatment plans. For this study, we will link the Finnish national population registry to the national comprehensive health care database to identify incident PD cases and a highly suitable comparison group, along with a wealth of covariate data for all subjects. We will further link these data with individual-level occupational data from the Finnish census and national pension database, and then estimate occupational solvent exposure, using the validated Finnish Job-Exposure Matrix (FINJEM). These Finnish databases have been used extensively to investigate occupational risk factors for many other diseases, including cancer and coronary heart disease, but remain to be used to investigate occupational risks associated with PD or other neurodegenerative diseases. The investigators and institutions in this proposal are ideally suited to perform the proposed study, representing the leading occupational health experts from the Finnish Institute of Occupational Health (FIOH) and well-established occupational epidemiology research collaboration between Washington University and the University of Washington.